I believe Bitcoin ATMs are just means for those who are too lazy to do normal research on how to buy bitcoin online
Believe it or not, some people don't want their banks/government know that they are buying bitcoin.
Most of them think it's an anonymous way of buying, which is far from that because the ATM captures their face and their mobile number is also taken.
If you are worried about cameras, you can always wear mask, sunglasses and baseball cap and pretty much completely hide your face and regarding the mobile number, not all BATM require that (at least not in Europe). I am not saying that its a best way to buy bitcoin/sell because it simply isn't, but I'll rather have more options than not.